1. Field of the Invention
The invention relates to a combustion-engined setting tool for driving fastening elements in a constructional component and including a reservoir for storing fuel or oxidation agent, a combustion chamber, a feeding conduit connecting the reservoir with the combustion chamber, at least one mechanically controlled valve arranged in the feeding conduit for controlling flow of the fuel or oxidation agent therethrough, and a switch element for time-delayed opening of the mechanically controlled valve in response to actuation of the switch element.
2. Description of the Prior Art
Combustion-engined setting tools of the type described above are well known. Such tools can be operated on both gaseous fuel or liquid fuel that is combusted in the combustion chamber for driving the tool drive piston that drives a fastening element in a constructional component.
In general, a problem with such tools consists in admixing of a properly proportioned amount of air or oxygen, which is used as an oxidation agent, to the fuel for each operational cycle. In particular, the air, which is drawn from the surrounding atmosphere, is subjected to pressure and temperature variations which can unfavorably influence the combustion of the fuel-air mixture when the mixture contains too much or too little fuel.
German Publication DE-42 43 617 A1 discloses a setting tool including a gas inlet valve which opens with mechanical means during an operational cycle to provide for flow of fuel from a fuel source in a storage chambre connected with the surrounding atmosphere. This connection permits to equalize the pressure and, if needed, the temperature in the chamber with those of the surrounding air, so that a properly proportioned fuel-air mixture reaches the combustion chamber. The fuel-air mixture is fed into the combustion chamber at a predetermined time. The drawback of this solution consists in that the connection with the surrounding air leads to some loss of the fuel.
European Patent EP-0 597 241 B1 discloses a combustion-engined setting tool in which the feeding of the fuel from a fuel source into a combustion chamber is controlled by a normally closed solenoid valve. The valve operation is controlled by a switching circuit which in response to actuation of a switch, opens the valve after a predetermined time delay to provide for flow of fluid from the fuel source into the combustion chamber.
The drawback of the setting, tool disclosed in EP-0 597 241 B1 consists in that the tool becomes inoperative when the electronic control falls, e.g., the power source becomes discharged or one of electronic components becomes defective. In case of any failure, the valve remains closed.
Accordingly, an object of the present invention is a setting tool of the type described above in which the drawbacks of the prior aft setting tools are eliminated.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a combustion-engined setting tool including at least one mechanically controlled valve arranged in the feeding conduit for controlling flow of the fuel or oxidation agent therethrough, a switch element for time-delayed opening of the mechanically controlled valve in response to actuation of the switch element, and at least one normally open electronically controlled valve likewise arranged in the feeding conduit for controlling the flow of the oxidation agent or fuel from the reservoir into the combustion chamber.
The normally open, electronically controlled valve is preferably arranged, in the flow direction of the fuel or the oxidation agent, downstream of the mechanically controlled valve. The electronically controlled valve remains open, in particular, when the electronic control circuit for controlling the electronically controlled valve falls, e.g., due to an interruption of voltage supply. The mechanically controlled valve can be open in response to action of mechanical controlling means, e.g., trigger, nose button switch, magazine switch, and so forth, alone or in combination. The predetermined opening time period of the mechanically controlled switch can be so selected that the fuel-air mixture would contain an excess of fuel so that an optimal combustion could not be achieved. However, the mixture can still be ignited, so that in case of failure of the electronics, the setting tool is still operative.
Advantageously, the predetermined opening time period of the mechanically controlled valve is so selected that during an operational cycle, that time period exceeds the maximal flow-through time period of the fuel through the electronically controlled valve which flow-through time is determined by an electronic control circuit for each operational cycle a new dependent on predetermined parameters.
Advantageously, there is provided a flow meter for measuring an amount of fuel flowing into the combustion chamber. The flow meter communicates with the control circuit. The control circuit processes the information supplied by the flow meter and closes the electronically controlled valve when the amount of fuel measured by the flow meter reaches, during the operational cycle, an optimal value.
In order to adapt the amount of fuel to the surrounding environmental conditions, e.g., to the temperature, air pressure, and air humidity, there is provided sensor means for determining the environmental condition parameters.
The sensor means generates corresponding signals and communicate them to the control circuit. The control circuit determines, for each operational cycle, a set amount of fuel to be fed into the combustion chamber in accordance with the determined parameters of the environmental conditions. The sensor means can include sensors for determining air pressure, temperature, and humidity of surrounding air.
With the electronically controlled valve being formed as a piezo valve, a more rapid reaction time in response to the control signal is achieved, providing for a correct and error-free closing and opening of the valve.
Advantageously, the control circuit includes a parameter processing unit which is formed as or includes a microprocessor.
Proper proportioning of the fuel-air mixture can be obtained, in case the reservoir contains an oxidation agent, by controlling the flow of the oxidation agent into the combustion chamber in a manner described above with reference to controlling the flow of the fuel. Moreover, the proportioning of the fuel-air mixture can be effected by both controlling the flow of fuel and controlling the flow of the oxidation agent.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.